Though great progress has been made in astronomy in the past fifty years, ______ still much that remains mysterious to astronomers _______ the universe, even the solar system [ ]

__________ she sing English songs—Yes, she can.

Word has come ___ a 100-million-year-olddinosaur fossil was recently discovered on a mountain in Ningcheng County,Chifeng.

It’shigh time you had your hair cut ; it’s getting .

His best-known work that is ___ all praisecan be seen in the museum．